Results: Both PRK and LASIK induced significant forward shifts of the cornea. Corneal forward shift was progressive up to 6 months after PRK, but no progression was seen after LASIK. Progressive thinning and expansion of the cornea were not observed after either procedure. The amount of corneal forward shift showed a significant negative correlation with preoperative corneal thickness (r = -0.586; P < 0.01) and a significant positive correlation with the amount of myopic correction (r = 0.504; P < 0.01). A significant correlation was found between the amount of forward shift and the degree of myopic regression after surgery (r = -0.347; P < 0.05).

Conclusion: Myopic PRK and LASIK induce significant forward shifts of the cornea, which are not true corneal ectasia. Eyes with thinner corneas and higher myopia requiring greater ablation are more predisposed to anterior protrusion of the cornea. Corneal forward shift was progressive up to 6 months after PRK but not progressive after LASIK. Forward shift of the cornea can be one of the factors responsible for myopic regression after surgery.

Last edited by Bill on Wed Feb 15, 2006 2:21 am, edited 1 time in total.

PURPOSE: To prospectively assess the forward shift of the cornea after laser in situ keratomileusis (LASIK) in relation to the residual corneal bed thickness.

SETTING: Miyata Eye Hospital, Miyazaki, Japan.

METHODS: Laser in situ keratomileusis was performed in 164 eyes of 85 patients with a mean myopic refractive error of -5.6 diopters (D) +/- 2.8 (SD) (range -1.25 to -14.5 D). Corneal topography of the posterior corneal surface was obtained using a scanning-slit topography system before and 1 month after surgery. Similar measurements were performed in 20 eyes of 10 normal subjects at an interval of 1 month. The amount of anteroposterior movement of the posterior corneal surface was determined. Multiple regression analysis was used to assess the factors that affected the forward shift of the corneal back surface.

CONCLUSIONS: Even if a residual corneal bed of 300 microm or thicker is preserved, anterior bulging of the cornea after LASIK can occur. Eyes with thin corneas and high myopia requiring greater laser ablation are more predisposed to an anterior shift of the cornea.

Department of Ophthalmology and Visual Science, College of Medicine, Catholic University of Korea, Seoul, Korea.

Purpose: To describe the morphological features of a prominent ectasia of the cornea after laser in situ keratomileusis (LASIK).

Methods: The morphology of the ectatic corneas was examined using corneal topography, light microscopy and transmission electron microscopy in 2 cases who underwent penetrating keratoplasty due to poor visual acuity induced by progressive corneal ectasia after LASIK.

Results: On topographic examination, the apex of the corneal surface was observed within the central 3-mm zone, and the smallest thickness was 0.116 and 0.271 mm in each case. On histological examination, the epithelial layer became thinner and detached easily. Bowman's membrane was broken down and folded. An irregular arrangement of the stromal lamellae with fibroblastic keratocytes was found. The fulled fiber cell, a transformed epithelial cell, was visible in a plane on Bowman's layer in the central region. In contrast, the corneal endothelium was intact, and no abnormality was found in both cases.

Conclusion: On morphological examination of 2 cases with corneal ectasia, a forward protrusion of both the anterior and posterior corneal surfaces occurred, and epithelial detachment, Bowman's membrane breakage and folding and irregular lamellae were found. The 2 cases had greatly thinned and protruding corneas, yet there was no abnormality in the corneal endothelium.

Comparison of Forward Shift of Posterior Corneal Surface after Operation between LASIK and LASEK.

Kim H, Kim HJ, Joo CK.

Department of Ophthalmology and Visual Science, College of Medicine, The Catholic University of Korea, Seoul, Korea.

Purpose: To compare the forward shift of the posterior corneal surface as a function of time after surgery between successful laser in situ keratomileusis (LASIK) and laser-assisted subepithelial keratectomy (LASEK).

Methods: Twenty-two eyes from 14 patients who underwent LASIK and 19 eyes from 10 patients who underwent LASEK were reviewed retrospectively. The uncorrected visual acuity, spherical equivalent and pachymetry were obtained before and 1 or 2 weeks and 2, 6, 12, and 24 months after surgery. The change in the elevation of the posterior corneal surface was assessed using the difference map of an Orbscan II (Bausch and Lomb, Salt Lake City, Utah, USA), which was generated from the preoperative and subsequent postoperative elevation map.

Results: One or 2 weeks after LASIK and LASEK, the posterior corneal surface had shifted forward by 18.00 and 25.90 mum, respectively (p = 0.008). However, the mean posterior corneal surface reduced by 3.05 mum from 1 or 2 weeks to 2 years in the LASIK group (p = 0.359). In contrast, the mean posterior corneal surface had reduced by 12.40 mum in the LASEK group (p = 0.004). This forward shift did not return to the corneal normal elevation observed prior to surgery in the two groups.

Conclusions: Refractive surgery induced a forward shift of the posterior corneal surface early postoperatively in the LASIK and LASEK groups, and this change after LASEK was significantly larger than that observed after LASIK. The posterior corneal surface gradually shifted backwards depending on the time course in both groups, but they did not return to the preoperative levels.

We report a case of corneal ectasia detected 32 months after laser in situ keratomileusis (LASIK) for correction of -4.25 diopters (D) of myopia associated with -2.00 D of regular but slight asymmetric astigmatism. The patient retained stable visual acuity for 15 months postoperatively. The preoperative corneal thickness was 540 microm, and the postablation untouched stroma was assumed to be 290 microm. Although a rare complication of LASIK, corneal ectasia can occur, and there is no consensus regarding how much stroma should be left intact to avoid it. Until we have a better understanding of corneal strength, we think surface photorefractive keratectomy or laser-assisted subepithelial keratectomy ablations should be considered instead of LASIK in borderline cases.

_________________Broken Eyes

"The price good men pay for indifference to public affairs is to be ruled by evil men." Plato

PURPOSE: To report corneal histopathology associated with keratectasia after laser in situ keratomileusis (LASIK) and to evaluate the thickness of the calculated residual stromal bed in two cases and those in the literature. DESIGN: Interventional case reports. METHODS: Three eyes of two patients developed keratectasia after LASIK. Corneal specimens after penetrating keratoplasty in one eye of each patient were studied histopathologically, and the residual stromal bed was directly measured. For comparison, residual stromal bed thicknesses were calculated from published cases of keratectasia. RESULTS: Two eyes of a 26-year-old woman and one eye of a 22-year-old woman developed keratectasia after LASIK. Calculated residual stromal bed thicknesses were 210, 213, and 261 microm. Histologic sections revealed focal scarring in the flap plane. The cornea specimens measured 75 and 118 microm thinner than calculated values immediately after LASIK. Transmission electron microscopy of one case revealed an average lamellar thickness of 0.94 microm. In 28 (49%) of 57 previous cases of keratectasia, the calculated residual stromal bed thicknesses were greater than 250 microm. CONCLUSIONS: Both the flap and the stromal bed of the cornea may thin after LASIK. A residual stromal bed thickness of 250 microm does not preclude the development of keratectasia after LASIK.

_________________Broken Eyes

"The price good men pay for indifference to public affairs is to be ruled by evil men." Plato

We report a case of corneal ectasia detected 32 months after laser in situ keratomileusis (LASIK) for correction of -4.25 diopters (D) of myopia associated with -2.00 D of regular but slight asymmetric astigmatism. The patient retained stable visual acuity for 15 months postoperatively. The preoperative corneal thickness was 540 microm, and the postablation untouched stroma was assumed to be 290 microm. Although a rare complication of LASIK, corneal ectasia can occur, and there is no consensus regarding how much stroma should be left intact to avoid it. Until we have a better understanding of corneal strength, we think surface photorefractive keratectomy or laser-assisted subepithelial keratectomy ablations should be considered instead of LASIK in borderline cases.

_________________Broken Eyes

"The price good men pay for indifference to public affairs is to be ruled by evil men." Plato

PURPOSE
To measure the imprecision of microkeratome cuts, preoperative corneal pachymetry, and laser ablation depth and develop a statistical model to describe the probability of the residual stromal bed thickness (RST) after myopic LASIK being significantly thinner than predicted.

METHODS
Preoperative corneal thickness, flap thickness, ablation depth, and RST were measured in 36 eyes by a prototype three-dimensional very high-frequency (VHF) 50 MHz digital ultrasound scanning device (<1.2 ?m precision), precursor to the commercially available Artemis 2. All eyes had undergone LASIK with the Moria LSK-One microkeratome and the NIDEK EC-5000 excimer laser. Based on the statistically combined uncertainty (standard deviation) and bias (accuracy to intended value) of corneal thickness measurement, flap thickness, and ablation depth, a continuous probability function was devised describing the chance of obtaining an actual RST less than a specified ?cut-off.? The model was applied using the data collected from the cohort of eyes. The model was also applied using published flap thickness statistics on a series of microkeratomes.

RESULTS
Precision (standard deviation) was 0.74 ?m for VHF digital ultrasound measurement of pachymetry, 30.3 ?m for Moria LSK-One flap thickness, and 11.2 ?m for NIDEK EC-5000 ablation depth. Assuming negligible laser ablation depth bias, the model found the probability that the actual RST will be <200 ?m given a target RST of 250 ?m is 7.56% with the Moria LSK-One. The model applied to published flap statistics revealed a range of probabilities of leaving <200 ?m given a target RST of 250 ?m from <0.01% to 33.6%.

CONCLUSIONS
The choice of microkeratome, laser, and pachymeter has a significant impact on the variation of the depth of keratectomy and thus on the risk of ectasia. This model together with high-precision microkeratomes, preoperative pachymetry, and knowledge of laser ablation precision would enable surgeons to determine the specific imprecision of RST prediction for individual LASIK cases and minimize the risk of ectasia. [J Refract Surg. 2006;22:851-860.]

Drs Reinstein, Silverman, Sutton, and Coleman have a proprietary interest in the Artemis technology (Ultralink LLC, St Petersburg, Fla) through patents administered by the Cornell Research Foundation, Ithaca, NY. The remaining authors have no proprietary or financial interest in the materials presented.

Some of the aspects of this study were presented at the Association for Research in Vision and Ophthalmology Annual Meeting; May 9-14, 1999; Fort Lauderdale, Fla.

Preparation in partial fulfillment of the requirements for the doctoral thesis, University of Cambridge, for Dr Reinstein.

Flap Quality in Single vs. Multiple Use of the Same Blade in the Flapmaker Microkeratome

M?dis et al

Quote:

A recent study by Seitz et al6 suggested that a mild, probably non-progressive keratectasia of the cornea may be common at 3 months after LASIK and may depend on the residual bed thickness. According to previous reports, the residual corneal thickness should not be less than 250 μm to avoid clinically significant progressive iatrogenic keratoconus and devastating optical distortion.7-9

_________________Broken Eyes

"The price good men pay for indifference to public affairs is to be ruled by evil men." Plato

Several short-term and long-term complications have been reported, with the most worrisome the development of post-LASIK ectasia.

Quote:

Although there are many recommendations to avoid ectasia, there have been no definitive studies to establish a ??safe?? RSBT to avoid ectasia.

Quote:

The incidence of post-LASIK ectasia is yet to be established.

Quote:

If we bear in mind that more than 17 million patients globally (34 million eyes) and 8 million (16 million eyes) in the United States have had LASIK to date (source: David Harman, Market Scope, Minnesota, USA) and based on the studies cited above as well as this current study, one would expect to have a possible 20,400 to 112,200 post-LASIK ectasia cases globally and 9600 to 52,000 in the United States alone.

_________________Broken Eyes

"The price good men pay for indifference to public affairs is to be ruled by evil men." Plato

PURPOSE
To report a case of ectasia occurring >4 years following LASIK with no risk factors and a residual stromal bed >300 ?m.

METHODS
A 33-year-old woman presented 4 years after LASIK with mild blurring in the left eye. Uncorrected visual acuity (UCVA) had been 20/20 in both eyes previously.

RESULTS
Uncorrected visual acuity was 20/20 and 20/40 in the right and left eyes, respectively. Best spectacle-corrected visual acuity (BSCVA) was 20/20 with ?0.75 +2.25 X 70? refraction in the left eye, which matched topography. Preoperative corneal thickness was 595 ?m, and topography showed no risk factors preoperatively or immediately postoperatively. Calculated residual stromal bed was 342 ?m and measured 400 ?m with ultrasound microscopy. One year postoperatively, UCVA decreased to 20/400, and BSCVA decreased to 20/60 with refraction of ?4.50 +5.00 X 90?. The patient was intolerant of contact lens wear and is considering collagen cross-linking, Intacs, or corneal transplantation.

CONCLUSIONS
Ectasia can occur more than 4 years after LASIK. Its etiology is unknown and management is challenging. [J Refract Surg. 2007;23:620-622.]

This report shows that ectasia can occur >4 years following uncomplicated LASIK in a patient with no risk factors.

Quote:

Confocal microscopy of corneas after LASIK have shown 20% loss of keratocytes above and below the flap interface by apoptosis immediately following surgery, which progressed to 40% at 5 years postoperatively.6 This loss of keratocytes has been seen in histology specimens of corneas removed during keratoplasty for ectasia.7 The decrease in keratocytes could progressively weaken the stromal bed and cause ectasia. It is conceivable that individual corneas differ in stromal keratocytes density, and the loss of keratocytes could cause ectasia in corneas with fewer keratocytes. Although most people develop ectasia much earlier, a weakened stromal bed may explain its developmentin our patient 4 years after LASIK.

Quote:

Management of ectasia after LASIK is challenging due to its rapid progression. The use of contact lenses may correct vision but could be diffi cult to fi t, and patients may be intolerant due to dry eye, as was our patient.

Quote:

One third of ectasia cases following LASIK require penetrating keratoplasty. 1 However, penetrating keratoplasty may result inunacceptable lifestyle changes in patients who often choose LASIK due to their active lifestyle. Also, a large graft may be necessary to include the entire LASIK flap and the donor cornea would be sutured to an intactrecipient rim, which would increase risk of rejection. Other options are implantation of intrastromal rings (Intacs) and riboflavin with collagen cross-linking.8,9 However, these merely stabilize the cornea, and visiondoes not improve to the same levels noted before ectasia. In addition, cross-linking involves ultraviolet light, and its long-term effects are unknown.

_________________Broken Eyes

"The price good men pay for indifference to public affairs is to be ruled by evil men." Plato

PURPOSE: To analyze the epidemiologic features of ectasia after excimer laser corneal refractive surgery, to identify risk factors for its development, and to devise a screening strategy to minimize its occurrence.

DESIGN: Retrospective comparative and case-control study.

PARTICIPANTS: All cases of ectasia after excimer laser corneal refractive surgery published in the English language with adequate information available through December 2005, unpublished cases seeking treatment at the authors' institution from 1998 through 2005, and a contemporaneous control group who underwent uneventful LASIK and experienced a normal postoperative course.

RESULTS: There were 171 ectasia cases, including 158 published cases and 13 unpublished cases evaluated at the authors' institution. Ectasia occurred after LASIK in 164 cases (95.9%) and after photorefractive keratectomy (PRK) in 7 cases (4.1%). Compared with controls, more ectasia cases had abnormal preoperative topographies (35.7% vs. 0%; P<1.0x10(-15)), were significantly younger (34.4 vs. 40.0 years; P<1.0x10(-7)), were more myopic (-8.53 vs. -5.09 diopters; P<1.0x10(-7)), had thinner corneas before surgery (521.0 vs. 546.5 mum; P<1.0x10(-7)), and had less RSB thickness (256.3 vs. 317.3 mum; P<1.0x10(-10)). Based on subgroup logistic regression analysis, abnormal topography was the most significant factor that discriminated cases from controls, followed by RSB thickness, age, and preoperative corneal thickness, in that order. A risk factor stratification scale was created, taking all recognized risk factors into account in a weighted fashion. This model had a specificity of 91% and a sensitivity of 96% in this series.

CONCLUSIONS: A quantitative method can be used to identify eyes at risk for developing ectasia after LASIK that, if validated, represents a significant improvement over current screening strategies.

BE's comment: This tells me that the 250 RSB rule is NOT safe. Why are they still using it and how are they getting away with it? This is an example of the LASIK industry ignoring medical literature and continuing to do business as usual, keeping the standard of care low and ignoring patients' best interest.

_________________Broken Eyes

"The price good men pay for indifference to public affairs is to be ruled by evil men." Plato

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